1. Field of the Invention
The present invention relates to an optical module that provides individual housing for an optical processing unit and an optical sub-assembly.
2. Related Prior Art
It is known that, in an optical transmitting module, a laser diode (LD) is driven by a DC signal and an external modulator modulates un-modulated light emitted from the LD. Since the LD is driven by the DC signal, a spectral width of the emitted light becomes narrow, especially when using the DFB-LD (Distributed Feed-Back LD) and driving the DFB-LD by the DC signal, the spectral width thereof can be narrowed to scores of GHz. A Mach-Zehnder modulator is combined to such DFB-LD for modulating the light emitted from the DFB-LD.
According to FIG. 16, which is a schematic diagram showing a conventional module having the Mach-Zehnder device as an external modulator, the module 1 provides single housing 3, within which the LD 5 and the Mach-Zehnder device 7 is installed via a bench 9. Some additional components, such as lenses 15, 17, and 19, and an optical isolator 13, are also mounted on the bench 9. On the bench 9, the Mach-Zehnder device 7, the LD 5, lenses 15, 17, and 19, and the optical isolator 13 are optically aligned to each other.
In the optical module shown in FIG. 16, the optical alignment between the LD and the Mach-Zehnder device is carried out by lenses disposed therebetween. However, the alignment in a XZ-plane, namely in a plane parallel to the primary surface of the bench 9, is relatively simple compared to the rest direction Y. By sliding the lens on the bench 9, the alignment in the XZ-plane can be done. Nevertheless, for the direction Y, the alignment must be carried out to adjust the level of the optical axis of the lenses 15, 17, and 19. The adjustment of the level is done by the machining of the base of the lens after measuring the height of the optical axis of the LD 5 and the Mach-Zehnder device 7 from the bench 9. The adjustment by the machining must be performed for respective lenses. Thus, the alignment along the direction Y contains complex procedures.
The alignment accuracy of the conventional module 1 along the Y-direction of the lens is fully determined by the measurement of the level of the optical axis and the machining of the base. The critical accuracy is a few micron meters at least, which is insufficient for the module using the single mode fiber. Accordingly, additional lens 21 may be prepared on the edge of the optical isolator to optically couple the LD 5 to the Mach-Zehnder device 7 in effective.
Further, even in the alignment in the XZ-plane, the sliding of the lens is carried out by using a manipulator. Accordingly, a space for operating the manipulator must be prepared between the LD 5 and the isolator 13, and between the isolator 13 and the Mach-Zehnder device 7, which restricts to position the lens 17 close to the isolator 13.